Cationic polymeric compositions have typically been prepared in acidic mediums. For example, U.S. Pat. No. 3,399,159 discloses the preparation of cationic latices by polymerizing, in an acidic medium with a pH between 1 and 3.5, a nitrogen monomer of the vinylpyridine or tert-butylaminoethyl methacrylate type and an alkyl acrylate in the absence of an emulsifier.
Similarly, U.S. Pat. No. 3,253,941 discloses cationic latices obtained by polymerizing, in an acidic medium, an aminoalkyl monomer, such as alkylaminoalkyl acrylates or methacrylates, a monomer of the styrene, vinyltoluene, acrylonitrite, or methyl methacrylate type, and a C.sub.1 -C.sub.8 acrylic ester.
However, the latices obtained from these processes cannot be used in a basic medium, because the cationic charge density is too low when the medium is at a basic pH. In addition, because the polymer particles of the aqueous dispersions of these processes are unstable, a significant percentage of undesirable grains is formed during the polymerization or neutralization of the aqueous dispersion. The presence of these undesirable grains decreases the quality of the dispersions and increases production costs by reducing yield.
Thus, an object of the present invention is to prepare aqueous cationic dispersions of synthetic polymers with less than 500 parts per million (less than about 0.05% by weight of polymer) of undesirable grains and which can be used at any pH.